[Fix] AudioCodecModel training fails with PTL 2.0

[anteju]

Currently, AudioCodecModel training fails on main due to changes in PTL 2.0.

What does this PR do ?

This PR is fixing two issues when using PTL 2.0.

Collection: TTS

Changelog

• Support for training_epoch_end has been removed in v2.0.0, and we use on_train_epoch_end
  • Reference: Remove memory-retaining epoch-end hooks Lightning-AI/pytorch-lightning#16520
• Enable the detection of unused parameters in DDP, either by setting the string value strategy='ddp_find_unused_parameters_true'
  • Reference: Remove memory-retaining epoch-end hooks Lightning-AI/pytorch-lightning#16520

Usage

N/A

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Additional Information

• Related to Upgrade to pytorch lightning 2.0 #6433

[anteju]

This change is included in #7188.
Closing the PR.